EP0726354B1 - Dryer group of a dryer section for web material and use of a dryer group to gradually reduce the vapor pressure in the interior of the web - Google Patents

Abstract

The drying group of the drying section of a machine for a web material, and especially a papermaking machine, has a number of permeable drying blankets (9,11,13,15) at the drying cylinder (1), passing round it over each other, with at least two blankets at different positions on the peripheral surface of the drying cylinder (1). Pref. the drying blankets (9,11,13,15) have different permeabilities, decreasing from the lowest level at the drying cylinder (1), outwards. The angle (a-d) round the drying cylinder (1), covered by the drying blankets (9,11,13,15), decreases outwards from the lowest level. The strength of the innermost blanket (9) is less than the others (11,13,15), and it is finer and/or thinner than them. The drying blankets (9,11,13,15) are applied simultaneously or in succession to the web material. The system uses 2-4 blankets, in a drying group in a single row, with alternating drying cylinders and deflection rollers in separate rows, using drying suction rollers for the path deflection. The drying cylinders and the deflection rollers have about the same dia..

Description

The invention relates to a drying group Dryer section for sheet material, in particular a paper machine, according to the generic term of Claim 1 and the use of a drying group a dryer section for sheet material the features of claim 10.

For example in DE 44 16 585 A1 are several a dryer section forming dry groups are shown, each of which has a large number of heatable drying cylinders as well as an endless pressure belt (in the following also known as a dryer), which is the one to be dried Press the material web against the drying cylinder. Basically, single-row are from the prior art and two-tier dryer groups known. At The material web runs in a single-row dryer group meandering alternating around drying cylinders and deflection rollers. Here comes when going through Dryer group only one side of the material web in Contact with the drying cylinder surface while the other side of the material web from the pressure belt is supported.

In a two-row dryer group, the Material web also a meandering web, however, each from a drying cylinder one row to the following drying cylinder the other row of drying cylinders. Consequently one side of the material web comes into contact with the drying cylinders of the one row and the other side in contact with the drying cylinders the second row of drying cylinders. Usually is each of the two rows of drying cylinders Pressure band assigned to the material web each presses against the drying cylinder surface.

Be in a dryer section of a paper machine often single-tier and double-tier dryer groups used in combination to improve the material properties, such as shrinkage behavior and to influence the strength of the web.

A further increase in material web strength can be achieved in that the temperature in A value of, if possible, inside the material web reached over 100 ° C. For this, gas-fired are often used Drying cylinders used, the temperatures of approx. 300 ° C. Through additional use of tightly tensioned, fixed pressure tapes the vapor pressure inside the material web increases to a high value compared to the ambient pressure. However, this gives rise to the problem that when lifting the pressure belt from the surface of the material web the one prevailing inside the material web Vapor pressure suddenly relaxed. In places Bursting of the material web or in the worst case a web break is the result of this sudden steam escape from the interior of the material web.

A drying section is included in WO 92/20860 A1 a two-tier dryer group for drying one Paper web, which comprises several drying cylinders, over which the material web together with each one assigned to a row in the drying group Conveyor belt is guided. Some of the drying cylinders is an additional, second conveyor belt assigned to the outside of the web of material conveyor belt pressing against the drying cylinder is present. The additional conveyor belt that the drying cylinder in a relatively small size Wraps around the circumferential area, serves the pressure on the outer circumference of the drying cylinder Increase material web. The first and second Conveyor belts are at different circumferential positions removed from the drying cylinder.

By strongly pressing the paper web against the Drying cylinders are supposed to dry the paper web more evenly can be reached across the transport direction.

The object of the invention is to propose a drying group in which a burst the material web and / or a web break easily prevented. Another goal the invention is a use to be specified for the drying group.

This task is carried out using a drying group solved the features mentioned in claim 1. At This dryer group becomes several dryer fabrics used the one above the other a drying cylinder loop around each with different angles. Because at least two of the several Dryer screens in different positions from Drying cylinders are removed, the steam pressure gradually dismantled inside the material web, so that the material web bursts respectively tearing of the paper web is reliably prevented can be. The dry group stands out characterized in that the dryer fabrics are different Have permeabilities, the respective permeability - seen from the drying cylinder - from decreases inside out. Because of the different Permeability of the dryer fabrics can be gradually reducing the vapor pressure in the Further improve the inside of the material web.

In particular, through use, for example of three or more dryer fabrics, one after the other can be led away from the drying cylinder the contact pressure acting on the material web decrease gradually, increasing the vapor pressure can also gradually dismantle. With a preferred one Exemplary embodiment has the drying cylinder seen from outermost dryer fabric one Permeability from zero to.

In a further advantageous embodiment of the Invention is the innermost dryer fabric finer and / or thinner than further out Dryer fabrics. With the fine right on the Material web overlying dryer fabric can be a very good smooth surface structure of the material web achieve. Because with such fine dryer fabrics no large screen tensions can be reached, are used for the dryer fabrics that are further out firmer or thicker dryer fabrics used, which allow higher screen tensions.

Enclose in a further embodiment of the invention the outer dryer fabrics a smaller one Area of the drying cylinder as more inside Dryer fabrics. Preferably the Wrapping angle of the individual dryer fabrics -from Drying cylinder seen from the outside in to.

The invention can be in both single row and be provided in two-tier dryer groups.

Further advantageous configurations of the drying group result from the subclaims.

A use is also used to solve the problem a dryer section of a dryer section for web-like Material, especially a paper machine, proposed with the features of claim 10. The dry group includes at least one Drying cylinder made up of several dryer fabrics is partially entwined, one on top of the other Drying cylinders are guided, the web-shaped Material between the drying cylinder and the -from Drying cylinder seen from the innermost dryer fabric is guided and with at least two dryer fabrics at different circumferential positions from the drying cylinder be removed for gradual reduction the vapor pressure inside the material web.

Figur 1

schematisch einen Ausschnitt aus einer einreihigen Trockengruppe;

Figur 2

schematisch einen Ausschnitt aus einer weiteren einreihigen Trockengruppe;

Figur 3

schematisch einen Ausschnitt aus einer zweireihigen Trockengruppe;

Figur 4

schematisch einen Ausschnitt aus einer mehrere Trockengruppen umfassenden Trokkenpartie und

Figur 5

schematisch einen Ausschnitt aus einer weiteren Trockenpartie.

The invention will now be described with reference to exemplary embodiments and the drawing. Show:

Figure 1

schematically shows a section of a single-tier dryer group;

Figure 2

schematically a section of another single-tier dryer group;

Figure 3

schematically a section of a two-tier dryer group;

Figure 4

schematically a section of a drying section comprising several drying groups and

Figure 5

schematically a section of another dryer section.

A drying cylinder 1 and two shown in Figure 1 this adjacent deflection rollers 3 and 5 are part a single-tier dryer group. Usually there is such a single-tier dryer group consisting of several for example arranged in a row Drying cylinders and several deflecting rollers. Drying cylinder and deflection rollers are arranged in such a way that the paper web meanders the Drying group runs through, the paper web alternately the guide rollers and drying cylinders passed.

In the exemplary embodiment shown, a paper web is running 7 first around the deflection roller 3, then around the Drying cylinder 1 and then the other Deflection roller 5. The one wrapped by the paper web 7 Angle a on the drying cylinder 1 or Wrapping area depends on the distance respectively the arrangement of the two guide rollers 3 and 5. In this by the wrap angle a defined wrapping area is heated the paper web 7 over the lateral surface of the Drying cylinder 1 instead. Usually this becomes the inside of the drying cylinder is fed with steam. However, higher temperatures should be reached be, for example of about 300 ° C, so you go for gas firing of the cylinders, i.e. one Combustion of gases inside the cylinder, about.

In addition to the first endless dryer fabric 9 are three additional in the area of the drying cylinder 1 Endless dryer fabrics 11, 13 and 15 are provided. All three dryer fabrics 11, 13 and 15 are via a common deflecting roller 17 with the first Dryer screen 9 merged at a common point 19. Thus in this area lie on the Paper web 7 first the dryer fabric 9, then that Dryer 11, the dryer 13 and the very outside the dryer 15.

The contact pressure exerted on the paper web 7 consequently consists of the individual of the four Dryer screens 9, 11, 13 and 15 generated power components together.

After a wrap angle b becomes the outermost Dryer screen 15 via a deflection roller 21 from the drying cylinder 1 removed and another deflection roller 21a returned to the deflection roller 17.

In the same way, the dryer fabric 13 is used Deflection rollers 23 and 23a according to a wrap angle c and with the dryer 11 over deflection rollers 25, 25a and 25b according to a wrap angle d procedure. The dryer fabric 9 alone remains even when the deflection roller 5 rotates in contact with the paper web 7.

From Figure 1 it is clear that the wrap angle a of the innermost dryer fabric 9 am is greatest while the wrap angle d, c, b of the successive dryer fabrics 11, 13, 15 gradually get smaller.

With this configuration according to the invention the contact pressure acting on the paper web 7 gradually reduce, b all four dryer fabrics 9, 11, 13 and 15 rest and thereby applied the greatest contact pressure becomes zero at the end of the angular range becomes. So there are four different pressure zones Z1, Z2, Z3 and Z4.

If the paper web 7 runs into the printing zone Z1, so it is subjected to a very high contact pressure, so that a particularly good heat transfer is given from the drying cylinder 1 to the paper web 7. This also means that the Water vapor forming warmth inside the web cannot escape. The consequence is a high one Vapor pressure versus ambient pressure. In the Pressure zone Z2 the contact pressure is slightly reduced, which also lowers the vapor pressure. Another Reduction of contact pressure and vapor pressure in the Paper web interior takes place in the printing zone Z3 and then in the pressure zone Z4, here the Difference between vapor pressure inside the web and the ambient pressure is already relatively low is.

When subsequently removing the paper web 7 from Drying cylinder 1 is due to the aforementioned low vapor pressure does not lead to bursting the paper web 7, since a large part of the Vapor pressure previously in pressure zones Z2 and Z3 or Z4 relax respectively some of the steam could escape.

An increase in that caused by the pressure zones Effect can be achieved that dryer fabrics 9, 11, 13 and 15 with different permeabilities to get voted.

In pressure zone Z1 you want a high pressure or have a high water vapor pressure. For this reason, the outermost dryer fabric web 15 is included a permeability of 0, i.e. impermeable to water vapor, chosen. The permeability of the underlying Dryer fabrics 13, 11, 9 then take off the web to train to so that the water vapor permeability from pressure zone Z2 to pressure zone Z4 step by step increases. This also allows the Gradually reduce the steam pressure to a value, the harmless with regard to the bursting of the paper web is.

By choosing a very fine first dryer fabric 9 can be effectively prevented on the one that comes into contact with the dryer fabric Paper web 7 screen marks on the paper web surface form. Those with such finer ones Drying sieves are realizable sieve tensions very small, but can be increased by the others then correspondingly more powerful dryer fabrics 11, 13 and 15 can be compensated.

In Figure 2, another embodiment of the Dry group shown, which in turn is a single-tier dryer group. Compared to Figure 1, however, are several in a row Drying cylinder 1 and several dryer fabric suction rolls 27 shown.

In this embodiment, instead of the previous one described four dryer fabrics only three Dryer screens 9, 11 and 13 used. In contrast to the example shown in Figure 1 individual dryer fabrics 9, 11 and 13 not after each Drying cylinder returned, but only on End of the drying group.

Otherwise the basic structure corresponds to this Embodiment that shown in Figure 1. Here too, in addition to the paper web 7 accompanying dryer fabric 9 two additional dryer fabrics 11 and 13 used at the beginning of a Converge drying cylinder with dryer fabric 9 and after different wrap angles c and d can be removed from the drying cylinder. Are between the individual drying cylinders 1 the dryer fabric 13, the guide rollers 23 and that Drying screen 11 assigned to the deflecting rollers 25. Through the appropriate arrangement of these guide rollers can the respective wrap angle c or d set per drying cylinder 1 become. Furthermore, the two dryer fabrics can be 11 and 13 via the deflecting rollers 23 and 25 also successively on the drying cylinders apply, as shown in Figure 2 for the rear Drying cylinders can be seen clearly. At the end the drying group will be the two additional Dryer screens 11 and 13 on the common guide roller 23 removed from the last drying cylinder 1 and led to the beginning of the dry group.

The operation of this embodiment corresponds that of Figure 1, which is why on a repeated description omitted here becomes.

In contrast to the arrangement shown in Figure 1 are instead of the simple guide rollers 3 and 5 so-called dryer fabric suction rollers 27 are used. These have suction zones 29 which are in that circumferential area of the rollers on which the dryer fabric lies 9 and the paper web 7 are passed.

With the help of these dryer fabric suction rolls the paper web 7 in the area of the suction zones 29 to the Suction dryer fabric 9. Due to the increased Frictional forces of the paper web on the dryer fabric shrinkage is prevented or reduced. In addition there is a flutter of the paper web 7 avoided when rotating the dryer fabric suction roll.

From Figure 2 it can also be seen that the Diameter of the dryer fabric suction rolls 27 approximately Diameters of the drying cylinder 1 correspond. in the Comparison to the exemplary embodiment shown in FIG. 1, the drying cylinder diameters are something smaller and the deflection roller diameter, that is Suction roll diameter got bigger. Such Adjusting the diameter leads on the one hand to a particularly wide looping of the drying cylinders through the paper web 7 with the result of an improved Heat transfer from the drying cylinder to the Paper web. On the other hand, the dryer fabric suction rolls be made stiffer so that a The longitudinal tension of the dryer fabric can be increased is.

Due to the higher dryer fabric longitudinal tension and an increased contact pressure on the paper web, their strength can be increased Increase the compaction of the material.

An exemplary embodiment is shown in FIG which the principle of the invention on a double row Dry group is applied. As already mentioned, a two-tier dryer group usually sits consisting of drying cylinders arranged in two rows 31 and 41 together. The paper web 7 passes through the dry group alternating in a meandering pattern from a drying cylinder 31 of the upper row to a drying cylinder 41 of the lower row, etc.

Each drying cylinder row are, according to the Drying fabrics 9, 11, 13 and 15 of Figure 1, drying fabrics 32, 33, 34 and 42, 43, 44 respectively.

At the beginning of the two-tier dryer group, this will be Dryer screen 32 via a deflection roller 35 with the paper web 7 merged and after a wrap angle a on the drying cylinder 31 via a further deflection roller 35a removed. This deflection roller 35a in turn serves to bring the Dryer screen 32 closest to paper web 7 Drying cylinder 31 of the upper row of drying cylinders. This process is repeated until the last one Drying cylinder 31 of the top row, with a deflecting roller 35c the dryer fabric 32 to the beginning of the Dry group returns.

Deflection rollers corresponding to the deflection rollers 35a, 35b 36a, 36b and 37a, 37b are the Dryer screens 33 and 34 assigned. Only the feeder at the beginning of the drying group and return at the end of the drying group each via a common deflecting roller 38 or 38a accomplished.

Through a correspondingly offset arrangement of the deflection rollers 35a, 36a, 37a and 35b, 36b and 37b is a different wrap around the Drying cylinder 31 through the dryer fabrics 32, 33 and 34 reached as already related with the figures 1 and 2 described in detail has been. The wrap angle c of the extreme Dryer screen 34 is the smallest, the wrap angle a of the innermost dryer fabric 32 the biggest. The effect of this different Wrap angle was also extensively based on of the embodiment of Figure 1 explained. We will therefore repeat the description waived.

Since the two-row dryer group shown in Figure 3 is constructed symmetrically, that of lower drying cylinder row 41 associated drying screens 42 to 44 in the same way by means of deflection rollers 45 to 48 according to the dryer fabrics the upper row of drying cylinders.

In Figure 4 is a section of a schematic Dryer section shown, the several in a row switched single and double row dryer groups 51, 53, 55 and 57.

The paper web, for example coming from an upstream press section, first runs into the two-row dryer group 51 and is heated there. In the subsequent single-row dryer group 53, in which the drying cylinders are at the top, the paper web is heated more and is pressed against the cylinders more strongly than in dryer group 51 by means of increased dryer fabric tension (arrow S) in order to achieve good heating and compression of the material. In this example, only the last two drying cylinders of dryer group 53 are assigned the plurality of dryer fabrics according to the invention, while in FIG. 2 several dryer fabrics run over all cylinders 1 of the dryer group.

In the subsequent single-tier dryer group 55 of Figure 4, in which the drying cylinder in the lower Row are arranged, the paper web again applied with an increased contact force, wherein the several dry sieves according to the invention are assigned to two drying cylinders that arranged in the front area of the dryer group are.

The end of the dryer section can then be a double row Form dryer group 57.

In the embodiment shown in Figure 4 are those that interact with the multiple dryer fabrics Drying cylinder of drying group 53 and the dryer group 55 each gas-fired to higher temperatures in the range of approx. 300 ° C reach, then on these drying cylinders the risk of bursting without the invention Dryer fabrics would be particularly large.

FIG. 5 shows an exemplary embodiment similar to FIG. 4, however, in the single row Differences in groups 53 and 55 can be seen are. In the drying group 53 are all drying cylinders assigned two dryer fabrics during the Drying cylinders of dryer group 55 three dryer fabrics, corresponding to the example shown in FIG. 2, assigned.

Of course, the present invention can that means the assignment of several dryer fabrics to a drying cylinder within a drying group or a complete dryer section as desired respectively. The stake is not just on that single row dry groups shown in Figures 4 and 5 limited. So it's also possible to provide a double-tier dryer group in which both the top and bottom rows of Drying cylinders several drying screens one above the other assigned.

Claims (11)

1. Dryer group of a dryer section for web-like material, in particular of a paper making machine having at least one dryer cylinder (1), around which a plurality of dryer screens are partly wrapped and which are guided above one another around the dryer cylinder, wherein the web-like material (7) is guided between the dryer cylinder (1) and the innermost dryer screen (9) - viewed from the dryer cylinder (1) - and wherein at least two dryer screens are taken off at different circumferential positions from the dryer cylinder (1), characterized in that the dryer screens (9, 11, 13, 15) have different permeabilities, with the respective permeability reducing from the inside to the outside - seen from the dryer cylinder (1).
2. Dryer group in accordance with claim 1, characterized in that the innermost dryer screen (9) is made finer and/or thinner than dryer screens (11, 13, 15) lying further outwardly.
3. Dryer group in accordance with one of the preceding claims, characterized in that the wrapping angle (a to d) of the individual dryer screens (9, 11, 13, 15) reduce from the inside towards the outside when seen from the dryer cylinder (1).
4. Dryer group in accordance with one of the preceding claims, characterized in that the strength of the innermost dryer screen (9) is lower than the strength of the dryer screens (11, 13, 15) disposed further outwardly.
5. Dryer group in accordance with one of the preceding claims, characterized in that the dryer screens (9, 11, 13, 15) are applied simultaneously or after one another onto the web-like material.
6. Dryer group in accordance with one of the preceding claims, characterized in that two to four dryer screens are used.
7. Dryer group in accordance with one of the preceding claims, characterized in that it is a single-row dryer group in which dryer cylinders and deflection rolls are alternately and respectively arranged in different rows.
8. Dryer group in accordance with claim 6, characterized in that the deflection rolls (27) are formed as dryer screen suction rolls.
9. Dryer group in accordance with claim 7 or claim 8, characterized in that the diameter of the dryer cylinder and of the deflection rolls are approximately the same.
10. Use of a dryer group of a dryer section for web-like material, in particular of a paper making machine, having at least one dryer cylinder (1), around which a plurality of dryer screens (9, 11, 13, 15) are partly wrapped and are guided above one another around the dryer cylinder (1), wherein the web-like material (7) is guided between the dryer cylinder (1) and the innermost dryer screen (9) - viewed from the dryer cylinder (1) - and wherein at least two dryer screens are taken off from the dryer cylinder (1) at different peripheral positions for the step-wise reduction of the vapour pressure in the interior of the material web.
11. Use of a dryer group of a dryer section in accordance with one of the preceding claims 1 to 9 for the step-wise reduction of the vapour pressure in the interior of the material web.

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